Issue34

S. Kikuchi et alii, Frattura ed Integrità Strutturale, 34 (2015) 261 - 270; DOI: 10.3221/IGF-ESIS.34.28

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Figure 9 : A xonometric drawing of fracture surfaces of the (a) IP and (b) Harmonic series ( R = 0.1).

{0001} {0110}

Analyzed

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Propagation

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{1230}

Coarse-grained structure

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Figure 10 : Inverse pole figure (IPF) maps of the crack profiles in the Harmonic series ((a) R = 0.1 and (b) R = 0.5). Estimation of the threshold stress intensity range of the material with harmonic structure Based on these results obtained in the present study, one might expect that a fine-grained structure in the harmonic structure dominates the fatigue crack propagation of the Harmonic series. To quantify the effects of fine-grained structure on the fatigue crack propagation of Ti-6Al-4V alloy, the threshold values of  K obtained from the bulk homogeneous materials are re-plotted against the square root of the grain size, d in Fig. 11. For each R value, the value of  K th increased with square root of the grain size. The relation between  K th and d in the bulk homogeneous material are expressed as Eqs. (3) and (4), respectively.

 K th

= 2.86 + 0.578 d 1/2 : R = 0.1

(3)

 K th

= 2.61 + 0.259 d 1/2 : R = 0.5

(4)

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